Fun but flawed...

I've really enjoyed the game. A good variety of cannons and power-ups and I like the nautical theme however there's a fatal flaw for me. In the second of the two oceans that are in the game the later maps have ship bugs that make some maps unwinnable. Some ships crash into the base two or three cannon towers before the base. Some repair ships become invisible and freeze as soon as they are hit. These two issues can be overcome through replay and luck. The main problem is an invisible ship appeard that cannot be sunk. The damage bar is at minimum and stays there. It happens consistently on different waves on map 2-16. I've contacted the developer and got no response. It's not an expensive game but I'd like to be able to make it through to the end. I'd give it 5 stars if it worked or gets fixed.